Reservoir seal



H. R. FEHLING ETAL March 10, 1964 RESERVOIR SEAL Filed July 19, 1961 INVE N TORS HANS REQNHARD FEHLING f EDWARD HENRY HARVEY her ATTORNEYSUnited States Patent 3,124,107 RESERVGR SEAL Reinhard Fehling, Zug,Switzerland, and Edward Henry Harvey, London, England, assignors to LRP.Limited, London, England, a company of Great Britain Filed July 19,1961, Ser. No. 125,217 Claims priority, application Great Britain .luly30, 1960 Claims. (Cl. 120-42.4)

This invention relates to seals for liquid reservoirs in dispensinginstruments lor the like and, more particularly, to a new and improvedreservoir seal which is effective in all orientations of the reservoir.

This application is a continuation-impart of our copending applicationfor Seal for Reservoirs of Writing and Other Dispensing Instruments,Serial No. 5,872, filed February 1, 1960. In the copending applicationthere is described a seal for a liquid reservoir having a bore open atone end to the exterior of the reservoir comprising a solid followerpiston slidable in the bore having one end immersed in the reservoirliquid and forming a clearance space of capillary dimensions betweenitself and the walls of the bore. To balance the capillary and otherforces tending to draw the follower into the reservoir liquid, thecopending application discloses various arrangements for urging thefollower out of the reservoir liquid and, in one embodiment, acompression spring is provided inside the reservoir for this purpose.

In reservoir seals of this type, the spring exerts on the piston, in allorientations of the reservoir, a force tending to urge the piston `outof the reservoir liquid. As a result of this force the pressure in thereservoir is decreased by an amount corresponding to the capillarypressure set up by this force, thus tending to cancel the positive headof liquid in the reservoir. This eifect is most pronounced when thereservoir is nearly empty, in Iwhich condition the spring is almostfully compressed and there then arises a limitation as to the extent towhich the reservoir can be emptied under gravity.

`In a liquid reservoir for a writing instrument such as a ball-pointpen, it is highly desirable to convey the writing liquid to the writingextremity under a positive head, in order that the instrument shallfunction satisfactorily. Consequently, in a reservoir of the typereferred to, it becomes desirable to eliminate or at least reduce theeffect of the spring upon the piston in the normal writing attitude ofthe reservoir.

Accordingly, it is an object of the present invention to provide a newand improved reservoir seal which overcomes the above-mentioneddisadvantage of known seal arrangements.

Another object of the present invention is to provide a liquid reservoirseal which is uniformly effective in all orientations of the reservoir.

These and other objects of the invention are accomplished by providing,in a reservoir having a bore and a follower piston slidable in the borealong with an arrangement for urging the piston out of a liquid in thebore in all orientations of the reservoir, means for modifying the forceapplied by the urging arrangement when the reser- Voir is in a verticalorientation. In one embodiment of the invention, in which the urgingmeans is a compression spring within the reservoir, the means formodifying the force comprises a weight interposed between the spring andthe piston.

Further objects and advantages of the invention will be appa-rent from areading o-f the following description in conjunction i-with theaccompanying drawings, in which:

FIGURE l is a view in longitudinal section through a ball point writinginstrument having a reservoir seal ar- ICC ranged according to theinvention and positioned with the writing point downward;

FIGURE 2 is a view in longitudinal section through the instrument ofFIGURE l positioned With the writing point upward; and

FIGURE 3 is .a fragmentary vieaw in section through the relevant part ofthe reservoir of FIGURES 1 and 2 showing the relative attitudes of theWeight and follower when the reservoir is horizontal.

While the invention is applicable to reservoirs 0f writing instrumentssuch as fountain pens, stylographic pens, and ballpens and ball-pointpens, it is also applicable to dispensing instruments or applicators(primarily those having a ball-tip or ball-valve discharge end) such asmay be used for dispensing or applying deodorants, scent and othercosmetics. IIt is especially applicable to the reservoirs of ball-pointwriting instruments, for the diiliculties which the invention seeks toredu-ce have chielly arisen in connection with ball-point Writinginstruments.

In the representative embodiment of the invention shown in FIGURES l, 2and 3 the reservoir of a ballpoint writing instrument is numbered 10,the column of ink or other reservoir liquid A1-1, and the pistonfollower 12. The follower 12 is an easy sliding t in the bore and formsa capillary annular clearance with the wall of the bore. This clearanceis occupied by the liquid 11 which present-s a meniscus at the rear endof the annular clearance and thus forms a seal. If desired, a differentsealing liquid may be used. It is important that the follower 12 isslightly buoyant, i.e., its overall specific gravity or bulk density isslightly less than that of the Ireservoir liquid `11 in order that itdoes not sink. The interior of the reservoir constitutes the boreaforesaid; it is desirably of circular cross section and smooth.

In a reservoir seal of the kind thus far described, one end or face ofthe follower 12 is immersed in the reservoir liquid 11 whilst the otherend or face (usually subject to atmospheric pressure) emerges from theliquid with the result that at the latter end a small meniscus is formedat the surface of the thin annulus of liquid filling the clearancebetween the follower periphery and the reservoir wall.

If this meniscus is concave, the resulting capillary forces produce adepression (below atmospheric pressure) in this annulus of liquid. Inconsequence there is a pressure difference between the two faces or endsof the follower 12 which, even if the latter has the same bulk density(apparent specific gravity) as the liquid 11 tends to force the followerinto the liquid.

If this force is not balanced by an opposing force, the follower 12 willmove into the liquid 11 and extrude the latter through theabove-mentioned annular clearance. This condition normally exists whenthe Writing instrument lies on its side. Movement of the follower intothe liquid will continue until the concave meniscus changes its shape insuch a way that the resulting capillary forces no longer reduce thehydrostatic pressure in the reservoir, i.e., when in effect the pressuredifference between the two ends of the follower has vanished. Thecapillary pressure can only decrease if the radius 0f the meniscusincreases, i.e., if a strong, stable meniscus changes into a weak andusually unstable meniscus, whether slightly convex or slightly concave.When this happens there is danger of liquid seepage towards the rear endof the reservoir, especially if there already exists a film of liquid onthe reservoir wall behind the follower (as may happen due to the liquidlevel being lowered by the dispensing of liquid).

There is another and additional reason why there is danger of seepage.When the reservoir is lying on its side the annulus of liquid betweenthe follower periphery and the reservoir wall, at the lower part of thefollower periphery, is subjected to a positive hydrostatic head themagnitude of which is proportional to the diameter (or equivalentdimension) of the reservoir. Hence it is at this lower part of thefollower periphery that liquid seepage takes place, unless thehydrostatic head at each point of the annular surface of the liquid isbalanced by the local capillary pressure (depending on the local radiusof curvature of the liquid surface).

In this specification the expression strong meniscus" is used toindicate a meniscus which is very stable (and not one where the surfacetension force is particularly high, for surface tension is constant andindependent of curvature) the most important feature producing stabilityis a small radius of curvature, because such a meniscus will notpractically change its shape in various positions of the instrument. v

`In order to reduce the above-mentioned seepage of liquid, a compressionspring 20 is inserted in the bore of the reservoir to urge the piston 12out of the liquid 11 with a force insufficient to expel the followerfrom the liquid, as described in the above-mentioned copendingapplication. Inasmuch as the follower 12 is buoyant, however, the totalforce urging it out of the liquid 11 would be greater in the uprightposition shown in FIGURE 1 than in the inverted position shown in FIGURE2 in the absence of any means for modifying the force and this obviouslyimposes a limitation on the range of forces which can be applied to thefollower by the spring 20 without expelling it from the liquid.

In accordance with the present invention, therefore, there is insertedbetween the compression spring 20 and the follower 12 a ball 21 made ofheavy material, e.g. metal. The weight of this ball 21 is preferablysuch as fully to compress the spring as shown in FIGURE l when thereservoir is vertical with the writing point downward. When thereservoir is horizontal as shown in FIGURE 3, the ball 21 has no effecton the follower 12 since its weight is carried by the lower portion ofthe reservoir wall. When the reservoir is inverted, i.e., with thefollower downwards as shown in FIGURE 2, it is important that themaximum outward thrust of spring and ball 21 on the follower 12 shallnot be sufficient to eject the follower from the reservoir liquid, i.e.,the maximum outward thrust on the follower must not exceed the valuecorresponding to the maximum permissible pressure differential acrossthe liquid meniscus as set out in the copending patent application. Themaximum outward thrust occurs when the reservoir is almost empty and inthe inverted attitude, that is to say when the weight of the ball 21 isadded to the thrust of the spring 20 in its almost fully compressedcondition. It will be understood that the forces acting on the followermust be insufficient to overcome the capillary forces in the narrow gapbetween the ball and its housing. When changing the reservoir from thewriting position in which the follower is uppermost, to the horizontalposition, the ball 21 rolls along the reservoir under the influence ofthe spring 20. It is thought that this rolling action is advantageous inthat it avoids the sticking which might occur were the weight merelyslidable along the reservoir.

In a typical reservoir for a writing instrument made according to theinvention, the important dimensions were as follows:

Reservoir bore diameter mm-- 5.0 Follower diameter mm 4.9 Mean radialclearance mm 0.05 Length of uncompressed spring cm-- 7.5 Length ofspring when reservoir full cm 5.5 Number of turns 100 Mean diameter ofturns mm-- 4.75 Wire diameter of brass spring mm-.. 0.11 Spring rategm./cm 0.08 Specific gravity of ink I 1.1

Diameter of heavy ball mm 4.8 Specific gravity of heavy ball 8.95 Weightof heavy ball in air gm 0.52 Weight of heavy ball in ink gm 0.46

Buoyant force on follower when immersed in ink Maximum allowable outwardthrust on follower (corresponds to (Po-Pi)max condition) gm 1.1

Minimum allowable outward thrust on follower (corresponds to (Po-Pi)mincondition) gm 0.05

As is fully described in our copending application identified above, the(Po-Pi)max and (Po-Pi)min conditions are the conditions in which thepressure differential across the liquid meniscus surrounding thefollower is at the maximum and the minimum permissible values,respectively.

In operation, when the writing instrument is in the upright positionshown in FIGURE l, the follower 12 is urged out of the reservoir only bythe buoyant force acting on it, the spring 20 being compressed by theball 2l. In the inverted position shown in FIGURE 2, the weight of theball 21 and the force of the spring are combined to oppose the buoyantforce acting on the follower and urge the follower out of the reservoirwith sufficient force to balance the capillary force drawing it into theliquid. With the reservoir horizontal as shown in FIG- URE 3, thebuoyant force and the weight of the ball act only in the transversedirection and the force of the spring 20 is the only force urging thefollower out of the liquid.

Although the invention has been described herein with reference to aspecific embodiment, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchmodifications and variations are included in the intended scope of theinvention as defined by the following claims.

We claim:

l. A liquid reservoir including a seal comprising a conduit having aforward end and a rear end and having a bore of greater-than-capillarycross-sectional area which is subject to atmospheric pressure, pistonmeans slidable within the conduit and having a peripheral shape similarto but slightly smaller than that of the inside surface of the conduitso as to provide a space of capillary dimensions between the adjacentsurfaces of the piston means and the conduit, urging means effectivewhen the reservoir conduit is in a first position between horizontalorientation and an orientation wherein one of said rear end and saidforward end is lower than the other thereof for applying a component offorce to the piston means directed in the longitudinal direction of theconduit in a manner tending to thrust the piston means out of a liquidin the conduit which is suicient to balance any capillary forces tendingto draw the piston means into a liquid in the conduit, therebypreventing seepage of liquid through the space between the piston meansand the conduit, and means for modifying the component of force appliedby the urging means to the piston means when the reservoir conduit is ina second position wherein said other of said forward and rear ends islower than said one thereof, said modifying means being ineffective tovary the component of force applied by said urging means to said pistonmeans in said first position of said conduit.

2. A liquid reservoir according to claim 1 wherein the means formodifying the component of force applied by the urging means isresponsive to gravity.

3. A liquid reservoir according to claim 1 wherein the piston means hasa bulk weight which differs in one direction from that of a liquid to becontained in the reservoir conduit and the means for modifying theurging means component of force comprises a member movable within thereservoir conduit having a bulk weight which differs in the otherdirection from that of the liquid to be contained in the reservoir.

4. A liquid reservoir.` according to claim 1 wherein the r a 6 urgingmeans comprises a compression spring located Referen es Citer?. in thele of this patent Within the reservoir conduit.

NI TA P E T 5. A liquid reservoir according to claim 4 wherein the 1 UTEP s TES AT N Si means for modifying the urging means component of2,672,127 Fehlmg u Mar- 15 1954 force comprises a member movable withinthe reservoir 5 conduit having a bulk Weight greater than that of aliquid FOREIGN PATENTS to be contained in the reservoir interposedbetween the 1,138,908 France Feb. 4, 1957 compression spring and thepiston means.

1. A LIQUID RESERVOIR INCLUDING A SEAL COMPRISING A CONDUIT HAVING AFORWARD END AND A REAR END AND HAVING A BORE OF GREATER-THAN-CAPILLARYCROSS-SECTIONAL AREA WHICH IS SUBJECT TO ATMOSPHERIC PRESSURE, PISTONMEANS SLIDABLE WITHIN THE CONDUIT AND HAVING A PERIPHERAL SHAPE SIMILARTO BUT SLIGHTLY SMALLER THAN THAT OF THE INSIDE SURFACE OF THE CONDUITSO AS TO PROVIDE A SPACE OF CAPILLARY DIMENSIONS BETWEEN THE ADJACENTSURFACES OF THE PISTON MEANS AND THE CONDUIT, URGING MEANS EFFECTIVEWHEN THE RESERVOIR CONDUIT IS IN A FIRST POSITION BETWEEN HORIZONTALORIENTATION AND AN ORIENTATION WHEREIN ONE OF SAID REAR END AND SAIDFORWARD END IS LOWER THAN THE OTHER THEREOF FOR APPLYING A COMPONENT OFFORCE TO THE PISTON MEANS DIRECTED IN THE LONGITUDINAL DIRECTION OF THECONDUIT IN A MANNER TENDING TO THRUST THE PISTON MEANS OUT OF A LIQUIDIN THE CONDUIT WHICH IS SUFFICIENT TO BALANCE ANY CAPILLARY FORCESTENDING TO DRAW THE PISTON MEANS INTO A LIQUID IN THE CONDUIT, THEREBYPREVENTING SEEPAGE OF LIQUID THROUGH THE SPACE BETWEEN THE PISTON MEANSAND THE CONDUIT, AND MEANS FOR MODIFYING THE COMPONENT OF FORCE APPLIEDBY THE URGING MEANS TO THE PISTON MEANS WHEN THE RESERVOIR CONDUIT IS INA SECOND POSITION WHEREIN SAID OTHER OF SAID FORWARD AND REAR ENDS ISLOWER THAN SAID ONE THEREOF, SAID MODIFYING MEANS BEING INEFFECTIVE TOVARY THE COMPONENT OF FORCE APPLIED BY SAID URGING MEANS TO SAID PISTONMEANS IN SAID FIRST POSITION OF SAID CONDUIT.